As semiconductor devices and integrated circuits become more sophisticated and are required to provide more complex functions, precise junction control becomes a critical process requirement. That is, tight resistivity control and exact thickness with sharp nongraded junction control of the various regions comprising the semiconductor device become more crucial as the complexity increases. Generally, the more complex the function which the device is to provide, the more exact the process parameters must be, with smaller tolerances allowed for an operative device. To make such precisely characterized devices reproducible in large scale production, a manufacturing process is required which minimizes the process variables.
Techniques heretofore utilized in providing semiconductor electronic devices requiring exact process control have utilized conventional techniques, such as diffusion into an epitaxially grown layer, only with more stringent requirements on the diffusion process steps. That is, more precise control was required of the time, temperatures, surface concentrations of the dopant, and purity of the environment. Such techniques, however, do not lend themselves to large volume production and yet retain the exact process parameters required. Other processes developed include the "single support layer" technique over which this invention is an improvement, as described by U.S. Pat. No. 3,290,753, issued Dec. 13, 1966. Another process is the "double support layer" technique described in Electronic Industries, Vol. 24, No. 6, pp 38-42 (June 1965).
In bipolar semiconductor technology devices having precise resistivity control and thickness control are desired to minimize junction breakdown and leakage characteristics and for exact predictability of the completed device. For example, a bipolar transistor having precisely controlled, epitaxially grown, collector and base regions realizes the advantages of an abrupt junction unachievable by diffusion techniques. However, such a process has heretofore suffered from the inability to affectively contact the epitaxially grown regions and still contact an emitter region formed in the base region. Other bipolar devices, such as SCR's lateral transistors, and triacs obtain the advantage of such precise process control, heretofore related.
Field effect semiconductor devices also require exact resistivity and thickness control of the layers comprising the device, as the device becomes more sophisticated. That is, very tight channel thickness control and resistivity control allow more exact predictability of the characterization of the completed device when formed in a high volume production process.
Accordingly, it is an object of the present invention to provide devices and methods of producing them which provide tight junction control and resistivity control. It is another object of the present invention to provide semiconductor devices having tight process parametric control utilizing one or multiple epitaxially grown regions which are dielectrically isolated. It is still another object of the present invention to provide improved bipolar and field effect transistors both as discrete devices and in integrated curcuits by a process rendering tight process parameters for improved performance and for improved reproducibility.